This disclosure relates to a generator for a power generating system. In particular, the disclosure relates to an overvoltage limiting configuration and a method of limiting the output voltage of a generator to a desired voltage under overvoltage conditions.
One type of aircraft electrical power generating system includes a variable frequency generator. The variable frequency generator includes a permanent magnet generator (PMG), an exciter, and a main generator mounted for rotation on a common shaft. The shaft is driven by a prime mover.
A generator control unit (GCU) converts alternating current from the PMG to provide DC current to the exciter. Current from the exciter is fed to the main generator, which produces a voltage output.
Under some fault conditions, an overvoltage condition may result, which produces a higher than desired output voltage from the main generator. There are many strategies for limiting or preventing overvoltage conditions, but desired overvoltage protection remains lacking. For example, one typical overvoltage management strategy simply trips a switch to an open condition once a overvoltage threshold has been reached. Another strategy delays tripping the switch depending upon the duration of the overvoltage to avoid needlessly tripping the switch for a brief overvoltage spike. In both of the above strategies, once the undesired overvoltage has occurred, the generator is de-energized and effectively disabled, which may require the switch to be mechanically reset. Thus, the generator is not capable of supplying power during a persistent overvoltage condition.